GEOLOGY

Detailed explanation-1: -The color of a mineral’s streak is not always the same as the color of the mineral sample, as shown in Figure 4. Unlike the surface of a mineral sample, the streak is not affected by weathering. For this reason, streak is more reliable than color as an indicator of a mineral’s identity.

Detailed explanation-2: -A mineral’s streak can be different from its color. Golden pyrite leaves a greenish-black streak. But a particular mineral’s streak is always the same, no matter what its color. You could test clear, purple, and black pieces of quartz, and the streak will always be white.

Detailed explanation-3: -Streak is a more reliable property than color because streak does not vary. Minerals that are the same color may have a different colored streak. Many minerals, such as the quartz in the figure 3, do not have streak. To check streak, scrape the mineral across an unglazed porcelain plate (Figure 4).

Detailed explanation-4: -Some minerals leave a streak similar to their natural color, such as cinnabar, lazurite and native gold. Other minerals leave surprising colors, such as fluorite, which always has a white streak, although it can appear in purple, blue, yellow, or green crystals.

Detailed explanation-5: -A good example of this phenomenon is seen in the gems ruby and emerald where the same element can produce completely different colors. In these, trace amounts of Cr3+ replaces Al3+ and is responsible for the red color of ruby and the green color of emerald.